Method for continuously casting a hollow billet

ABSTRACT

Melted metal, typically copper, is applied through floating valve means to a water-cooled mold containing a mandrel of special form and materials so as to result in continuous downward movement of the solidified billet through the bottom lower end of the mold and over the lower end of the mandrel.

United States Patent 1 Arrington et al. Dec.,4, 1973 [54] METHOD FOR CONTINUOUSLY CASTING 3,51 1,304 5/ 1970 Baler et a]. 164/82 A HQLLOW BILLET 3,465,811 9/1969 Castelet 164/281 Inventors: Thomas B. Arrington; Leonard A.

Moody, both of Decatur, Ala.

Ass'ignee: Universal Oil Products Company,

Des Plaines, 111.

Filed: Apr. 24, 1972 Appl. No.: 246,644

Related US. Application Data Division of Ser. No. 134,953, April 19, 1971, Pat. No. 3,735,803.

US. Cl. 164/85 Int. Cl B22d 11/10 Field of Search 164/82, 85, 281

References Cited UNITED STATES PATENTS 10/1967 Baler 164/281 FOREIGN PATENTS OR APPLICATIONS 733,705 4/1943 Germany 164/281 751,356 5/1951 Germany 164/281 228,475 11/1943 Switzerland... 1647281 Primary Examiner-R. Spencer Atnnear Attorney-Donald P. Bush [5 7] ABSTRACT Melted metal, typically copper, is applied through floating valve means to a water-cooled mold containing a mandrel of special form and materials so as to result in continuous downward movement of the solidified billet through the bottom lower end of the mold and over the lower end of the mandrel.

4 Claims, 3 Drawing Figum Vii METHOD FOR CONTINUOUSLY CASTING A HOLLOW BILLET This is a division, of application Ser. No. 134,953 filed Apr. 19, 1971 now US. Pat. No. 3,735,803.

BRIEF SUMMARY OF THE INVENTION The present invention relates to continuous casting, and more particularly, to continuous casting of a hollow copper billet dimensioned for use in tube extrusion apparatus.

There is provided a relatively short cylindrical watercooled mold of substantial diameter as for example having an inside diameter in excess of 9 inches. Suspended from the top of the mold is a mandrel comprising a rod of heat resistant alloy, an upper sleeve of a re fractory material such for example as silica, and a lower sleeve of graphite. The lower graphite sleeve of the mandrel has an upper cylindrical portion, and a lower slightly tapered portion which prevents seizing as the solidification of the descending billet causes contraction thereof.

Molten copper is introduced into the annular space between the water-cooled mold and the mandrel from a downspout which is controlled by a vertically movable float valve the lower portion of which is received in the upper portion of the molten metal in the mold. As the level of the metal in the. mold moves downwardly in the continuous casting process, the float valve continuously meters the flow of molten metal into the mold to maintain the upper level of the surface of the molten metal at a substantially constant point.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of the continuous casting apparatus.

FIG. 2 is a side elevation, partly in section, of the structure shown in FIG. 1.

FIG. 3 is a sectional view on the line 33, FIG. 1.

DETAILED DESCRIPTION The apparatus comprises a water-cooled cylindrical mold having in a particular instance, an internal diameter of approximately 9 inches and a vertical height of somewhat in excess of 12 inches. This mold is suitably water-cooled by means, as for example, in the form of a water jacket 11 through which cooled water may be continuously circulated. The mold is supported with its axis vertical as best seen in FIG. 3, by suitable means such for example as the ring 12. Mounted on the ring 12 is a bridge ring 14 comprising two arcuate portions 16 interconnected by a transverse strut 18 which is horizontal across the top but has tapering bottom surfaces to provide increased central thickness as best seen in FIG. 2. The strut 18 is centrally apertured as indicated at 20 and receives an elongated headed bolt 22 formed of a suitable heat resistant metal alloy such for example as TZM molybdenum alloy, a molybdenum base alloy supplied by Climax Molybdenum Company. Other metals can be used however, and satisfactory results have been obtained using a nickel base super-alloy Inconel 718.

Mounted on the upper portion of the bolt 22 is a sleeve 24 formed of a suitable refractory material capable of operating in the severe chemical environment characteristic of the molten metal surface of the copper. Usually, there is a molten oxide slag floating on the upper surface of the molten copper including as a complex copper phosphorous oxide. Such a molten oxide severely attacks solid metal and graphite. Accordingly, the sleeve 24 is formed of a high temperature resistant material capable of resisting attack by the slag. An excellent material for this purpose is essentially a fused silica.

Referring to FIG. 3 it will be observed that the upper level of the molten copper is maintained by suitable means later to be described, approximately as indicated at L, and this upper surface of the molten metal where the slag is present, falls intermediate the upper and lower ends of the fused silica or other heat resistant and chemically inert sleeve 24.

The mandrel which is designated as a whole at M, has at its lower portion a sleeve 26 formed of graphite. The sleeves 24 and 26 are retained in end-abutment and the upper end of the sleeve 24 is in abutment with the lower surface of the transverse strut 18 of the bridge ring 14 by a washer 28 and nuts 30 threaded on the lower end of the bolt 22.

The refractory sleeve 24 is of external cylindrical configuration and in a typical example has a diameter of approximately 2 inches. The upper end of the graphite sleeve 26, as indicated at 32, has an external cylindrical sleeve equal in diameter to that of the refractory sleeve 24. The lower portion of the graphite sleeve, as indicated at 34, is slightly downwardly tapered and is connected to the cylindrical upper portion 32 by a small shoulder 36. In a typical embodiment of the invention the upper cylindrical portion 32 and the lower tapered portion 34 of the graphite sleeve are both 6 inches in length. The lower tapered portion diminishes from an outside diameter at the shoulder 36 from 1.86 inches to a diameter at its bottom end of 1.80 inches. The purpose of the taper is to accommodate shrinkage of the copper billet as it solidifies and moves downwardly so as to prevent seizure of the contracting billet on the mandrel. Above the shoulder 36 the molten cop per, while cooling, retains essentially a fluid character so that no taper is required on the upper portion 32 of the mandrel.

The molten metal is supplied to the interior of the mold 10 from a pan 40 having a tubular downspout 42 located centrally of and above the upper surface of the mold 10. In order to control the flow of molten metal through the downspout 42 so as to maintain the level L of the molten metal substantially as indicated at L, as the metal continuously solidifies and moves donwardly, there is a float 44. The float 44 is formed of a relatively light refractory material which can withstand the high temperature as well as the-chemical action of the molten copper, as well as the slag floating at its surface, and in addition is of a relatively light material so that it floats on the top of the molten copper.

The float is made from a castable refractory and chemically inert powder which may be essentially powdered silica. The powder is mixed with water, cast to desired form,-and fired in a furnace. The density of the material is less than 20 percent that of copper so that the float will extend substantially above the surface of the molten metal as shown.

The float 44 has a generally cylindrical exterior surface 46, a flat bottom surface 48, and a transversely downwardly open channel 49 having side surfaces 50 and a top surface 52. The channel 49 provides structure which permits the float to straddle the transversely extending strut 18 of the bridge ring 14.

Extending across the top of the float 44 is a transverse channel 54 the intermediate portion of which is deepened as indicated at 56 to have a bottom wall 58. Centrally of the bottom wall 58 is an upstanding cone 60 adapted to function as a valve element with the lower end of the downspout 42. The deepened intermediate portion 56 of the transverse channel 54 constitutes a reservoir which receives molten metal from the downspout 42 and this metal flows through vertical passages 62 connected by inclined passage 64 to the interior of the channel 49. It will be observed that with the parts in the position illustrated in FIG. 3, the outlet from the inclined passages 64 is substantially centered at the liquid level line L and the valving cone 60 is in closing relation to the downspout 42.

The float 44 floats on the upper surface of the molten metal and constitutes valving means which maintains the level as indicated in FIG. 3. As the metal in the mold l solidifies due partly to the cooling of the mandrel by the water-cooled mold 10, the molten metal solidifies gradually at a zone approximately at the shoulder 36 on the mandrel. As the substantially solidified metal of the billet continues to move downwardly and cools further, it undergoes shrinkage which is accommodated by the tapered shape of the lower portion 34 of the graphite sleeve. In addition, the graphite sleeve, while being capable of functioning at the elevated temperatures of the molten copper, also has the additional function of promoting downward movement of the solidifying billet due to its inherent characteristic of a solid lubricant.

In operation, molten metal may be added continuously through the downspout 42 at a rate controlled by the valve float 44 so as to permit continuous formation of the billet. The billet may be severed by suitable means into appropriate lengths for use in tube extrusion equipment.

While the actual dimensions of the mold and mandrel are not critical, a typical example has been given in the foregoing to emphasize the fact that the product is quite different from a conventional metal tube. It may be said that the outside diameter of thebillet should not be less than 6 inches, and the diameter of the opening through the billet should not exceed 3 inches.

We claim:

1. The method of continuously casting a hollow copper billet which comprises supporting an elongated mandrel of circular cross-section along the axis of a cylindrical mold positioned with its axis vertical and open at its top and bottom, the mandrel having an upper portion of a refractory material which is substantially chemically inert to attack by copper oxides, the portion of the mandrel below the said upper portion thereof having a surface which is graphite, feeding molten copper into the open top of the mold at an average rate to maintain the level of molten copper in the mold substantially constant and below the upper end of the lower portion of the mandrel which has a graphite surface, maintaining a layer of molten slag containing copper oxides over the molten copper with its lower surface above the lower end of the upper portion of the mandrel having a surface which is substantially inert to attack by copper oxides to prevent attack by such oxides on the graphite lower surface of the mandrel, and continuously moving the copper in the mold downwardly as it solidifies to discharge the solidified hollow copper billet continuously from the open bottom end of the mold.

2. The method of claim 1 in which the billet has an outside diameter in excess of 6 inches and an opening therethrough not greater than 3 inches.

3. The method as defined in claim 1 in which the refractory chemically inert material at the upper portion of said mandrel is fused silica.

4. The method of claim 1 in which the layer of slag comprises a complex copper phosphoric oxide. 

2. The method of claim 1 in which the billet has an outside diameter in excess of 6 inches and an opening therethrough not greater than 3 inches.
 3. The method as defined in claim 1 in which the refractory chemically inert material at the upper portion of said mandrel is fused silica.
 4. The method of claim 1 in which the layer of slag comprises a complex copper phosphoric oxide. 